Wikipedia (pronunciation(info • help)) is an Internet encyclopedia project in many languages. It is free of charge: users do not pay. Also, it is "open content". This means anyone can copy it, and anyone can edit it (write things in it). However, there are rules which must be followed for copying or editing.

Larry Sanger and Jimmy Wales are the ones who started Wikipedia.[5][6] Wales is credited with defining the goals of the project,[7][8] Sanger created the strategy of using a wiki to reach Wales' goal.[9] On January 10, 2001, Larry Sanger proposed on the Nupedia mailing list to create a wiki as a "feeder" project for Nupedia.[10] Wikipedia was launched on January 15, 2001. It was launched as an English-language edition at www.wikipedia.com,[11] and announced by Sanger on the Nupedia mailing list.[7] Wikipedia's policy of "neutral point-of-view"[12] was codified in its initial months, and was similar to Nupedia's earlier "nonbiased" policy. Otherwise, there were not that many rules initially and Wikipedia operated independently of Nupedia.[7]

Wikipedia gained early contributors from Nupedia, Slashdot, and also from search engines. It grew to about 20,000 articles, and 18 languages by the end of 2001. By late 2002 it had 26 languages, 46 by the end of 2003, and 161 by the end of 2004.[13] Nupedia and Wikipedia both existed till Nupedia's servers were stopped in 2003. After this, its text was incorporated into Wikipedia. The English Wikipedia passed the 2 million-article mark on September 9, 2007, making it the largest encyclopedia ever assembled, eclipsing even the Yongle Encyclopedia (1407), which had held the record for exactly 600 years.[14]

The English Wikipedia reached 3 million articles in August 2009. The numbers of articles and of contributors appeared to be growing less quickly around spring 2007.[15]

In October 2014, the Wikipedia Monument was unveiled to the public in Poland to honor all the contributors of the Wikipedia.

On January 15, 2011, Wikipedia celebrated its 10th anniversary. It used a special logo (pictured) to celebrate its 10 years since it opened on January 15, 2001, and the logo was used for the whole day on the sidebar of the English Wikipedia.